1. Field of the Invention
The present invention relates to a vibratory drive apparatus, for example, a rod-type vibratory drive apparatus including a piezoelectric member clamped between two elastic members, and a rotor configured to contact the piezoelectric member at one end and be frictionally driven by vibration excited in the vibrator.
2. Description of the Related Art
In general, a vibratory drive apparatus has applications for products, for example, for driving a camera lens, and there are two types of vibratory drive apparatuses: a ring-type vibratory drive apparatus and a rod-type vibratory drive apparatus.
A conventional rod-type vibratory drive apparatus (see Japanese Patent Application Laid-Open No. 2002-291263, for example) includes as its basic component a vibrator in which driving vibration is generated, and for example, the rod-type vibratory drive apparatus is configured to move the vibrator and a rotor, which is in contact with and pressed against the vibrator, relative to each other by the driving vibration.
The rod-shaped vibrator includes at least two elastic members and a piezoelectric element inserted between the at least two elastic members. In order to generate vibration efficiently, the piezoelectric element is clamped with predetermined clamping force. In such a configuration, an electric field is applied to the piezoelectric element to excite two mutually-perpendicular flexural vibrations in the vibrator, thereby inducing an elliptical motion on the elastic members. Then, a rotor which is pressed against the elastic members can receive frictional force as its driving force.
If an output of the vibratory drive apparatus is relatively large, i.e., the vibration of the vibrator is relatively strong, a portion of the piezoelectric element around a high stress point will be worn and the output of the vibratory drive apparatus may decrease.
The piezoelectric element is a ceramic sintered body which is made primarily of lead zirconate titanate, and generally has a lower hardness than those elastic members which are made of stainless steel. Thus, if the vibratory drive apparatus is driven and shearing force is exerted to the vicinity of the contact surfaces of the elastic members and the piezoelectric element, resulting in slight sliding between the elastic members and the piezoelectric element, the piezoelectric element will be worn. Wear debris produced then degrades adhesion and further introduces non-uniformity between the elastic members and the piezoelectric element. In addition, if the wear debris is produced unevenly, the horizontal-to-vertical ratio of the above mentioned elliptical motion on the elastic members will be large, resulting in a decrease in efficiency.
To address this problem, conventionally, the elastic members and the piezoelectric element need to be adhered to each other to eliminate the slight sliding and suppress the wear of the piezoelectric element.
Otherwise, a relatively soft thin plate made of aluminum, copper or the like is inserted between the elastic members and the piezoelectric element to relieve stress from concentrating on a certain point and thereby prevent the wear of the piezoelectric element.